This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The primary purpose of this study is to expand research on the effects of physical activity on basal metabolic rate (BMR) in healthy postmenopausal women, and to further compare the effects of long-term habitual exercise to the results of a shorter-term (16 weeks) training program. We will measure BMR by indirect calorimtery and normalize it across subjects for body size (fat free mass) and level of aerobic fitness (VO2MAX). Three groups will be compared: sedentary control group (never participated in regular exercise), formerly sedentary intervention group (no previous participation in regular exercise, newly enrolled in this study?s 16 week training program), long-term athlete group (have engaged in at least 5 hours of exercise per week for the past 10 years or longer). A secondary aim is to generate a regression equation for the prediction of BMR from fat free mass in physically active postmenopausal women, to be applied to hypotheses in biological anthropology. We expect to find at baseline that, controlling for fat free mass and VO2MAX, the control and intervention groups will not differ in BMR, while the long-term group will have significantly higher BMR. At 16 weeks we expect no change in BMR for the control and long-term groups, while BMR will have increased in the intervention group. At the same time, we expect to find a significant difference in BMR between the control and intervention groups, and expect that the intervention group will have BMR similar to that of the long-term athletes.